I have a GM 3/4 ton pickup.

I won, in an auction, a "Ramco RM5000" crane. This crane is similar to
the Harbor Freight truck crane, but is a lot beefier.

It is pictured he

http://igor.chudov.com/tmp/Ramco-RM5000-Truck-Crane.jpg

(not mine, but an identical model).

This is rated for 5k pounds, I am sure for the boom fully retracted.

It has a 8,000 lbs jack. I will put in a longer boom too, and a
winch. I am aware that extending the boom will decrease capacity
proportionally, so a boom that is 4 foot would decrease capacity of
the crane to, say, 1,500 lbs or whatever. I have to call the mfr to
find out. This is stillw ay better than my HF crane.

I have a very large 3/4 inch steel plate, I would say 3x4 feet, that
is rusting in my backyard.

What I thought of doing, is making a cutout on the plate to fit around
a wheel well, and mount it in the back of the truck's bed, and put the
crane on top of it. The Ramco crane would sit in the rear right corner
of the bed, just like this Harbor Freight crane does now:

http://goo.gl/KAN0Y

It has to be a large plate, to spread the weight of the crane and the
levering action that its base would apply to the bed. This particular
plate weighs around 300 lbs and is large enough.

My question is, what sort of constraints do I still have. I would hate
to overturn my truck, break suspension, etc. I would also think that
for heavy lifting, I would need to jack up the right rear wheel too.

Any practical opinions?

i